1. Field of the Invention
The invention relates generally to fasteners and more specifically, to fasteners having multiple mechanical advantages and capable of carrying relatively large loads.
2. Description of the Prior Art
Many thread forms varying in shape, pitch, and thread direction have been developed to provide finer adjustment with greater mechanical advantage or, conversely, fast lead screw designs having less mechanical advantage but providing the benefit of traveling farther with fewer turns. The disadvantage of all these present designs, when used on an externally threaded bolt turned into an internally threaded receptacle such as a nut, is the fact that both external and internal threads must be of the same size, shape, and pitch. Additionally, much of the time spent threading a bolt is spent threading under little or no load with a thread pitch having a greater mechanical advantage selected for the final end load. This wastes both time and energy. One response is to increase the pitch for a greater rate of travel. However, an additional drawback occurs when increasing pitch for a common bolt to obtain faster operation because the faster lead threads readily unthread under tension.
Fasteners for rapid fastening and release operations have been in use for a considerable period of time, especially in the aerospace industry. It is desirable that such fasteners be operable without special tools.
One particular fastener in general use today for quick take-up is the quarter turn fastener which is widely used to replace common screws and bolts. Such quarter turn fasteners suffer the drawback that they are typically quite limited in their reach or stroke. At the present time, use of threaded fasteners or elaborate latching mechanisms is limited to those applications where the components to be drawn together are spaced apart a distance of a couple of inches or less. Large "V" bands currently used for securing cowlings or other components in the housings of aircraft engines together require tightening through several inches into a preload condition of thousands of pounds and typically require high speed take-up.
In recognition of the need for a multiple speed take up fastener, a number of solutions have been proposed. One such device is described in U.S. Pat. No. 5,624,221 to the present inventor. This fastener includes a first and second pair of interengageable threaded members having different pitches and opposing thread directions. The first pair includes a first actuator with external fine lead threads for engaging the interior threads of a first thread plate. The second pair includes a second actuator which has coarse external threads engaged with the internal threads of a second threaded plate. A coupling assembly including a drive member, a driver member, an elongated rod, and a compression spring is provided to couple the first actuator with the second actuator. A bolt projects through and connects both pairs of interengageable members. Rotation of the bolt turns the fine thread of the first actuator and moves the first plate toward the second plate while at the same time turning the second actuator and second plate on opposite threads toward the first plate thereby drawing the attached structure together. As the two pairs approach, the spring disengages the drive member from the first actuator so that no further rotation of the second actuator will occur. From this point, only rotation of the first actuator is continued to draw the structures together on fine lead threads. While this device has proven satisfactory, the ability to perform a similar function with less moving parts in a smaller compact assembly still remains.
What is needed is a relatively simple bolt and receptacle assembly that combines the advantages of fast lead threads with fine lead threads with both threads running in the same direction and having a locking feature that resists the unthreading of the fast lead threads from vibrational and other load forces.